1. Technical Field
The present invention relates to power and clock supply management in a network workstation, more specifically to arrangements for initializing a network interface using clock sources from different power supply domains.
2. Description of the Related Art
Workstation computers are currently being designed to have multiple power supply domains, where a network interface within the workstation will remain in an operative state even though the host computer powers down into a standby state, for example, after a prescribed interval of inactivity. In such a case, internal logic within the workstation separates the externally supplied power into different power supply domains, for example a constant-supply domain that supplies power to selected components at all times that the workstation receives the externally supplied power, and a main power supply which powers the rest of the computer system in response to prescribed power supply conditions, for example a user pressing a power supply button, or reception by the network interface of a power management packet from a remote workstation.
Thus, the workstation may have a state where the network interface to a packet switched network may be operable based on a constant power supply, whereas the host computer (e.g., CPU) is in a standby mode, such that communication between the host computer and the network interface via a system bus is non-existent.
Network interfaces may typically be loaded at initialization with configuration information stored in a nonvolatile memory in response to a supplied clock, for example a PCI clock from the host computer or a network clock from the network. Conventional arrangements assume that the network interface during initialization has a state where both the host computer and the network are operable to enable configuration of the network interface. However, the segmenting of the network interface into a power supply domain that is separate from the respective power supply domains of the host computer and/or the network may cause a situation where the network interface enters an unknown state, since the network interface configuration registers are configured for loading configuration data in a prescribed sequence using a network transmit data clock or a network receive data clock. Hence, absence of either network interface clock when required may result in the network interface being inoperable without an entire system-wide reset of the workstation and the network in order to reinitialize the network interface according to the necessary sequence.
One common technique for resetting a system is to use asynchronous resets on the flip flops of internal configuration registers. However, use of asynchronous resets causes the problem that virtually all flip flops of this design need to be reset, resulting in a complete reload of the configuration registers. Moreover, the necessity of asynchronous resets results in a larger flip flop requiring more area on silicon.